The present invention relates to a technical field of pattern film formation by vacuum film formation. More specifically, the present invention relates to a pattern film forming method and a pattern film forming apparatus capable of forming a high-definition pattern film having a desired pattern and a sharp edge with high productivity.
Known methods of forming a pixel (illuminator) of an organic EL element are roughly classified into three kinds (combination of white electroluminescence and color filters, color conversion, and vapor-deposition with masking).
According to the combination of the white electroluminescence and color filters, a white organic EL layer is formed over the entire surface, and an R (red) filter, a G (green) filter, and a B (blue) filter corresponding to pixels are formed on the surface of the white organic EL layer, whereby light of three colors of R, G, and B is obtained. Furthermore, according to the color conversion, a blue light-emitting layer is formed over the entire surface, and a color conversion layer corresponding to pixels is formed on the blue light-emitting layer, whereby B-light is converted to R-light, and B-light is converted to G-light; thus, light of three colors of R, G, and B is obtained.
In both the methods, it is not necessary to form a patterned light-emitting layer, so that those methods are satisfactory in terms of productivity, and the like. However, according to the former method, filters cut off the unnecessary wavelength range, which decreases the light-emission efficiency. Furthermore, according to the color conversion, the efficiency of the conversion by the color conversion layer is low, which also decreases the light-emission efficiency.
On the other hand, according to the vapor-deposition with masking, light-emitting layers of respective colors of R, G, and B are patterned on the surface of a substrate, using a mask having a pattern corresponding to pixels (formation of a pattern film). Furthermore, as another method using a mask, JP 2003-173870 A discloses a method involving: forming a pattern film of a light-emitting layer on a transfer substrate using a mask; laminating together the transfer substrate and a substrate on which the light-emitting layer is to be transferred; and transferring the pattern film of the light-emitting layer onto the substrate, and a method involving: forming a light-emitting layer over the entire surface of a transfer substrate; laminating together the transfer substrate and a substrate on which the light-emitting layer is to be transferred through a mask; and transferring the light-emitting layer by heating, thereby forming a pattern film of the light-emitting layer on the substrate.
Thus, by forming a patterned light-emitting layer, individual pixels are allowed to emit light and can be controlled. Furthermore, there is no decrease in light-emission efficiency due to a filter and the like. Therefore, an image can be displayed with very high light-emission efficiency.
However, a very thin mask is necessary to form a preferable pattern film. Furthermore, a light-emitting layer formed of an organic EL element has usually a fine pattern, which makes the mask production difficult. Since the mask produced is thin and is easily broken, the handling properties in alignment and carrying are very poor. Furthermore, according to the method in which a film is formed by vapor deposition or the like using a mask, it is necessary to wash the mask each time film formation is conducted, which is laborious and may lead to breakage of the mask during washing. Display apparatuses are recently upsized. The larger the mask is, the more marked this problem is.
In contrast, a method in which a pattern film of a light-emitting layer is formed through transfer without using a mask is also known.
For example, JP 2918037 B discloses a method of producing a color organic EL display. This method includes the steps of: vapor-depositing a light-emitting layer (light-emitting organic material) on a transfer substrate having highly heat-conductive convex portions patterned in accordance with display pixels; clamping the transfer substrate onto a transparent conductive film substrate (or a positive hole transport layer formed on the transparent conductive film); and heating the convex portions on the transfer substrate to sublimate the light-emitting layer, thereby transferring the light-emitting layer onto the surface of the transparent conductive film substrate.
Furthermore, JP 2003-173870 A also discloses a method involving: forming a light-emitting layer by vapor deposition on an uneven surface of a band-shaped transfer substrate having irregularities corresponding to a pattern film of a light-emitting layer to be formed; and heating the transfer substrate from the side opposite to the uneven surface, thereby transferring the pattern film of the light-emitting layer to a substrate on which the pattern film is to be transferred.
However, according to the method disclosed in JP 2918037 B, a transfer substrate is heated to a high temperature close to 500° C. to transfer a film formation material to a substrate (substrate on which the film formation material is to be formed) by sublimation. Therefore, no pattern film made of a material having low heat resistance can be formed. Furthermore, in view of productivity, the material for the pattern film is limited to those which have satisfactory sublimation property and evaporation property, and heat resistance is also required in the transfer substrate; therefore, the range of choice for the material of the light-emitting layer and the transfer substrate are narrow and this method has no degree of freedom or versatility. Simultaneous sublimation in the periphery of pixels cannot be avoided. Therefore, pixels having sharp edge cannot be formed. Furthermore, this method discloses laser light as a preferable heating means, but it is difficult to keep the positional precision of laser irradiation, and it is also difficult to keep high productivity.
Furthermore, according to the method in which a light-emitting layer is formed on an uneven transfer layer by means of vapor deposition or the like, a light-emitting material that is not used is deposited in concave portions, so that it is necessary to wash the transfer substrate periodically, and furthermore, the light-emitting material deposited in the concave portions will become waste.
In contrast, according to the method of producing a pattern sheet through transfer, as disclosed in commonly assigned JP 2003-139944 A, the above-mentioned problem can be solved.
According to this method, a monochrome film is produced, in which a color ink layer obtained by coating/drying ink (coating) prepared by dissolving a polymer organic light-emitting material, a polymer binder, and the like in an organic solvent is formed on a film material; the monochrome film and a sheet as a substrate on which a pattern film is to be formed are laminated together so that the color ink layer comes into contact with the sheet; and the laminate thus obtained is pressed with a pressing member having irregularities corresponding to the pattern film to be formed, whereby the pattern film made of the color ink is formed on the sheet. According to the method disclosed in JP 2003-139944 A, monochrome films whose number corresponds to the number of colors for a pattern to be formed are produced and a multi-color pattern sheet is produced by successively transferring the monochrome films on the sheet.
According to the method disclosed in JP 2003-139944 A, a light-emitting layer having a pattern corresponding to pixels can be formed with high productivity by means of a simple facility and control without using a mask and without heating at high temperature and the like. Furthermore, the pressing member having irregularities corresponding to the pattern does not come into direct contact with the light-emitting layer (light-emitting material). Therefore, unlike the case where a film is formed on a transfer member with irregularities formed thereon, the waste of the material for the pattern film such as a light-emitting material can be prevented, and washing of the pressing member can also be made unnecessary.
However, according to the method disclosed in JP 2003-139944 A, since the adhesion between the film material and the color ink layer is high, the transfer property of the monochrome film onto the sheet is low, and the binding force in the film is strong, so that the color ink layer is unlikely to be broken. Therefore, for applications requiring high productivity, sharpness in the edge portion, and a-high-definition pattern, it is difficult to preferably apply the above method. Thus, there is a demand for a method of forming a pattern film capable of producing a pattern film having higher sharpness and higher definition with higher productivity.